Thanks Ron! As long as it's reasonably sharp in those mid-zone areas, I think I'll be good. I'm not a huge sharpness guy, but it doesn't hurt. My favorite lens, maybe ever, is the 58/1.4G ... so if the ASPH is as good or better across the frame at 1.4-2, I'll be happy.
I've actually wondered if the heavier brass construction could have any detrimental effects, like you mentioned. I think I'm going to go for it... under $2500 seems like a reasonably good deal for one in good shape. (Right?)